1. Field of the Invention
The invention relates to a magnetic resonance apparatus, comprising a magnet system for generating a steady magnetic field, a magnet system for generating mutually perpendicular gradient fields, and an r.f. coil for generating a spatially uniform r.f. magnetic field.
2. Description of the Prior Art
A magnetic resonance apparatus of this kind is known from an article in Computertomography 1, 1981, pages 2-10.
In an apparatus of this kind use is preferably made of a superconducting magnet system for generating the steady magnetic field, notably for apparatus involving a comparatively strong magnetic field, for example stronger than 0.5 T. The problem of high energy consumption for generating the steady field is thus circumvented. Because of its comparatively short switching times, it is difficult to construct a gradient coil system from superconducting coils. Therefore, the gradient coil system in known apparatus is one of the components having the highest energy consumption. The energy stored in such a coil system increases as the fifth power of the coil dimension. The smaller the coil is, the more efficient it will operate. A large amount of stored energy is unattractive not only because of the energy costs, but notably also because it impedes the realization of short switching times and an increasing number of disturbing phenomena occurs as the amount of energy required increases.
Known coil systems, for generating a uniform r.f. transmitter field in a comparatively large measuring space also require a comparatively large amount of energy. Moreover, the homogeneity of an r.f. field to be generated is affected by the presence of the gradient coils; a customary r.f. shield necessitates the use of complex and expensive power supply equipment.